Databases, Systems & Networks

If you read our previous article Easy Ubuntu Server Firewall, then you may have noted that on Ubuntu 16.04 the described method no longer works. This is due to systemd. In the article below we will walk through creating a persistent IPTables based firewall on Ubuntu 16.04 LTS. First we need to install some required software packages. As seen in the command below, install iptables-persistent. Next we will make netfilter-persistent run at boot. This is the most important step as it will ensure your rules are reloaded at boot time.

# Install IPTables Persistent Package
apt-get install -y iptables-persistent
# Add netfilter-persistent Startup
invoke-rc.d netfilter-persistent save
# Stop netfilter-persistent Service
service netfilter-persistent stop

Once the packages above are installed and the service is stopped, you will have a new directory at /etc/iptables/. This directory holds the IPTables filter rules that will be reloaded at boot time. These files are named rules.v4 and rules.v6 respectively. IPV4 rules are loaded into rules.v4 and IPV6 rules are loaded into rules.v6. For the purpose of this article we will focus on IPV4 rules. Next we will want to copy the rules below into our rules.v4 file. Of course the rules will need to be modified to fit your environment.

# Generated by iptables-save v1.3.3 on Wed Apr 9 10:51:08 2008
# Flush out any rules that are already in there
*filter
:INPUT ACCEPT [146:11332]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [104:9831]
 
# Allow internal loopback connections
-A INPUT -i lo -j ACCEPT
-A OUTPUT -o lo -j ACCEPT
 
# Allow pinging
-A INPUT -p icmp -m icmp --icmp-type 8 -j ACCEPT
 
# Allow any outbound data, and any inbound data related to a connection that is already in use
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A OUTPUT -m state --state NEW,RELATED,ESTABLISHED -j ACCEPT
 
# =========BEGIN SERVER SPECIFIC PORT OPEN RULES=========
# Allow SCP/SSH Access from Green & Blue Subnet
-A INPUT -s 172.16.12.0/255.255.255.0 -p tcp -m tcp --dport 22 -j ACCEPT
-A INPUT -s 10.10.12.0/255.255.255.0 -p tcp -m tcp --dport 22 -j ACCEPT
 
# Allow HTTP Access from Red Subnet/Internet
-A INPUT -p tcp -m state --state NEW,ESTABLISHED --dport 80 -j ACCEPT
 
# Allow HTTPS Access from Red Subnet/Internet
-A INPUT -p tcp -m state --state NEW,ESTABLISHED --dport 443 -j ACCEPT
 
# Allow MySQL Access from Red Subnet/Internet
-A INPUT -p tcp -m state --state NEW,ESTABLISHED --dport 3306 -j ACCEPT
 
# Allow FTP Access from Red Subnet/Internet
-A INPUT -p tcp -m state --state NEW,ESTABLISHED --dport 21 -j ACCEPT
-A INPUT -p tcp -m state --state NEW,ESTABLISHED --dport 58000:58010 -j ACCEPT
# =========END SERVER SPECIFIC PORT OPEN RULES=========
 
# Drop everything that hasn't been picked up by one of the rules above
-A INPUT -j DROP
-A FORWARD -j DROP
-A OUTPUT -j DROP
 
COMMIT
# Completed on Wed Apr 9 10:51:08 2008

Lastly, in order for our new rules to take affect, we simply need to start the netfilter-persistent service as seen below. That’s it, you now have a fully functional IPTables based firewall.

# Start netfilter-persistent Service
service netfilter-persistent start

# Check if IPTables were applied
iptables -L